io: add new qio_channel_{readv, writev, read, write}_all functions

These functions wait until they are able to read / write the full
requested data buffer(s).

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

include/io/channel.h

@@ -268,6 +268,58 @@ ssize_t qio_channel_writev_full(QIOChannel *ioc,
                                 size_t nfds,
                                 Error **errp);
 
+/**
+ * qio_channel_readv_all:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to read data into
+ * @niov: the length of the @iov array
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Read data from the IO channel, storing it in the
+ * memory regions referenced by @iov. Each element
+ * in the @iov will be fully populated with data
+ * before the next one is used. The @niov parameter
+ * specifies the total number of elements in @iov.
+ *
+ * The function will wait for all requested data
+ * to be read, yielding from the current coroutine
+ * if required.
+ *
+ * If end-of-file occurs before all requested data
+ * has been read, an error will be reported.
+ *
+ * Returns: 0 if all bytes were read, or -1 on error
+ */
+int qio_channel_readv_all(QIOChannel *ioc,
+                          const struct iovec *iov,
+                          size_t niov,
+                          Error **errp);
+
+
+/**
+ * qio_channel_writev_all:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to write data from
+ * @niov: the length of the @iov array
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Write data to the IO channel, reading it from the
+ * memory regions referenced by @iov. Each element
+ * in the @iov will be fully sent, before the next
+ * one is used. The @niov parameter specifies the
+ * total number of elements in @iov.
+ *
+ * The function will wait for all requested data
+ * to be written, yielding from the current coroutine
+ * if required.
+ *
+ * Returns: 0 if all bytes were written, or -1 on error
+ */
+int qio_channel_writev_all(QIOChannel *ioc,
+                           const struct iovec *iov,
+                           size_t niov,
+                           Error **erp);
+
 /**
  * qio_channel_readv:
  * @ioc: the channel object
@@ -330,6 +382,44 @@ ssize_t qio_channel_write(QIOChannel *ioc,
                           size_t buflen,
                           Error **errp);
 
+/**
+ * qio_channel_read_all:
+ * @ioc: the channel object
+ * @buf: the memory region to read data into
+ * @buflen: the number of bytes to @buf
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Reads @buflen bytes into @buf, possibly blocking or (if the
+ * channel is non-blocking) yielding from the current coroutine
+ * multiple times until the entire content is read. If end-of-file
+ * occurs it will return an error rather than a short-read. Otherwise
+ * behaves as qio_channel_read().
+ *
+ * Returns: 0 if all bytes were read, or -1 on error
+ */
+int qio_channel_read_all(QIOChannel *ioc,
+                         char *buf,
+                         size_t buflen,
+                         Error **errp);
+/**
+ * qio_channel_write_all:
+ * @ioc: the channel object
+ * @buf: the memory region to write data into
+ * @buflen: the number of bytes to @buf
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Writes @buflen bytes from @buf, possibly blocking or (if the
+ * channel is non-blocking) yielding from the current coroutine
+ * multiple times until the entire content is written.  Otherwise
+ * behaves as qio_channel_write().
+ *
+ * Returns: 0 if all bytes were written, or -1 on error
+ */
+int qio_channel_write_all(QIOChannel *ioc,
+                          const char *buf,
+                          size_t buflen,
+                          Error **errp);
+
 /**
  * qio_channel_set_blocking:
  * @ioc: the channel object